lecture 15 notes - Today in Astronomy 111: giant planets...

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27 October 2011Astronomy 111, Fall 20111Today in Astronomy 111: giant planetsand planetary atmospheresThe other giant planetsVitals of Saturn,Uranus and NeptuneGas giants and icegiantsVertical density andpressure structure ofatmospheresAll four giant planets, on the same scale(Voyager images, JPL/NASA).
27 October 2011Astronomy 111, Fall 20112Saturn’s vitalstatistics299-3214Mass5.684610gm (95.2)Equatorial radius6.026810cm (9.45)Average density0.687 gm cmMoment of inertia0.210Bond albedo0.3421.4335310cmOrbital semimajor axis(9.582 AU)Orbital eccentriciMRMR×××ty0.0565Obliquity26.73Sidereal29.457 yearsrevolution periodSidereal10.656 hoursrotation periodMoons62 and countingRings7 major ones°Saturn, fromCassini(JPL/NASA)
27 October 2011Astronomy 111, Fall 20113Visits to SaturnWe have visited Saturn fourtimes, including the visitcurrently in progress:Pioneer 11(1979)Voyager 1(1980)Voyager 2(1981)Cassini(2004-)TheVoyagerfamily portrait ofSaturn and some of its larger moons(JPL/NASA)
27 October 2011Astronomy 111, Fall 20114Saturn: structure and compositionLike Jupiter, Saturn is a gas giant.Has the lowest average density of the planets, and a verylow moment of inertia for its mass.Spins almost as fast as Jupiter, and its visible surface iseven more distorted by its rotation than Jupiter (polardiameter 10% smaller than equatorial diameter), owing tolower density and larger rocky core.Definitely has a rocky core,Elements heavier than H even more abundant than inJupiter; e.g..Visible constituents:96.3% H2, 3.25% He, 0.45% CH4, 0.013% NH3, 0.011% HD,0.0007% C2H6, 0.0004% H2O.T= 95 K at the cloudtops. Compare to 83 K expected fromheating by sunlight.~ 12.MC H10(C H)
27 October 2011Astronomy 111, Fall 20115Saturn: structure and compositionThus Saturn emits 2.5 times as much power as it receivesin sunlight, similar to Jupiter.Related to major abundance difference from Jupiter?There’s much less helium in Saturn’s upperatmosphere, leading to suggestions of formation andprecipitation of liquid helium droplets (helium rain)that gradually raises the density of the interior (thusreducing potential energy, increasing heat).

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Term
Fall
Professor
DanM.Watson
Tags
Astronomy, Solar System, Planet, Neptune

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